Who was the only British prime minister to die at 10 Downing Street?

Henry Campbell-Bannerman died at 10 Downing Street on 22nd April 1908, 19 days after he resigned as PM, to become the first former prime minister to die at 19 Downing Street.

https://en.wikipedia.org/wiki/Henry_Campbell-Bannerman

Ill health forced Campbell-Bannerman to resign, but he remained in Number 10 until he died almost three weeks later. He is the only PM to die in a place he once described as a 'rotten old barrack of a house'.

Spencer Perceval.

https://www.gov.uk/government/history/past-prime-ministers/spencer-perceval

"The early nineteenth century saw one of the most shocking events in the house's history. Lord Grenville's successor, Spencer Perceval, came to Number 10 in a carriage and left in a coffin.

"A high-flying lawyer, politician and family man, he arrived at Number 10 in 1807 as Chancellor of the Exchequer, and became prime minister two years later. His twelve young children - some born while he was prime minister - filled every spare room of the house.

"It made the events of 11 May 1812 especially tragic. Entering the lobby of the House of Commons in the late afternoon, Perceval was shot in the chest by a former convict with a grudge. His body was taken back to Number 10, where it lay for five days before the funeral."